Device for actuating a hydraulic power steering system

ABSTRACT

Apparatus for actuating a hydraulic power steering system for automotive vehicles, wherein the steering shaft (1 ) is allowed to roll off on the gear rack (3) to a small degree to actuate the steering valve. To enable this rolling motion, the steering shaft (1 ) is supported in a sleeve (9) which, in turn, is supported through needle bearings (10) so as to be rotatable in relation to the steering gear housing (4). To prevent inadvertent steering maneuvers in the event of partial or complete system failure, the needle bearing axis is arranged in parallel to the center line of the steering shaft (1) as well as in one plane with the steering shaft and with the point of force transmission between pinion (2) and gear rack (3). The needle bearing axis is radially outward from the central point of the steering shaft axis than the point of force transmission. A captivated spring (24) is provided to retain the valve slide (19) in its neutral position.

BACKGROUND OF THE INVENTION

The present invention relates to a device for actuating a hydraulicpower steering system for automotive vehicles having the followingfeatures:

A steering shaft, non-rotatably coupled with the steering wheel, isfurnished with a pinion and is supported in a sleeve,

The pinion is engaged with a gear rack coupled to the wheels to besteered,

The sleeve is supported in a steering gear housing so as to be pivotableabout an axis, parallel in relation to the steering shaft, and itcomprises a recess to enable the pinion to engage into the gear rack,and on it a pin-shaped extension is secured perpendicularly relative tothe steering shaft, the extension actuating the valve slide of asteering valve designed as a linear slide valve, and

A spring which presses the gear rack against the pinion andsimultaneously stabilizes the support of the sleeve in the steering gearhousing.

A device of this type is known from European patent application 0 291155. In this prior art device, the sleeve is supported on that side ofthe steering shaft in the housing which is remote from the gear rack.The bearing is formed by a spherical indentation in the extension and aspherical shell-shaped recess in the steering gear housing. Adisadvantage of this device is that high friction forces occur in thebearing because of the great radius of effect the friction force has dueto the spring being pressed on. However, the strong spring is requiredto ensure freedom of play between gear rack and pinion. Further, thesystem has a tendency of being unstable since the force of the spring,which keeps the gear rack in contact with the pinion, induces a rollingmotion of the steering shaft on the gear rack, the steering valve beingactuated as a result. This might be a safety risk since the vehiclewould be steered inadvertently in such a case.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to improve upon theknown steering actuating device such as to render it stable in theneutral position and to nevertheless permit its actuation almost withoutlosses due to friction. In addition, the inventive device is to have adegree of freedom of rotation solely in parallel to the steering shaftaxis.

This object is achieved by the combination of the following featureswith the known features:

The bearing between the sleeve and the steering gear housing is formedby two needles,

The two needle bearings are disposed on different sides of the gearrack, and

The bearing axis of the two needle bearings is farther away from thesteering shaft center line than the point of force transmission betweenpinion and gear rack, and it is placed on the same side of the steeringshaft center line as the latter point, and the valve slide is biassed bya captivated spring.

The design and arrangement of the needle bearings has, as a result, asmall radius of effect of the friction forces which are caused due tothe load on the spring, and thus permits an easy-motion actuation. Thecaptivated spring stabilizes the valve slide in its neutral position.

In an advantageous improvement of the present invention, each of theneedles is retained in an insert ring rigidly coupled to the steeringgear housing. This measure permits an easy assembly of the insert ringswith the needles in the steering gear housing. The second bearing partin the sleeve is formed in a straightforward fashion by annularextensions of the sleeve, fixed in relation to the needles by the forceof a spring. In addition, the insert rings simultaneously serve aslimiters (stops) for the rotary motion of the sleeve about the bearingaxis. This results in reliable prevention of large roll off motions ofthe steering shaft and sleeve on the gear rack which might cause damageto the steering valve, the steering gear housing or the teeth of thegear rack.

A particularly simple assembly is made possible by a radial extensionbeing screwed into a threaded bore of the sleeve. In this embodiment,the extension can be screwed in after the sleeve and steering shaft havebeen inserted into the gear housing.

In order to adjust a maximum possible valve travel in the event ofslight roll-off motions of the sleeve and steering shaft, expediently,the radial extension is arranged perpendicular relative to the gearrack.

Other embodiments of this invention provide that the end of the radialextension which is not coupled to the sleeve is furnished with aspherical joint and is received in a recess of the valve slide. Also,the housing of the steering valve is rigidly coupled to the steeringgear housing.

Apart from actuation of a steering valve, the inventive device can beused also to re-adjust the eccentricity of a pump which directly actsupon a double-effect hydraulic cylinder producing the auxiliary force,or to actuate an electric switch, a sliding contact, a potentiometer orsensor of an electric or electrohydraulic power-assisted steeringsystem, respectively.

The present invention will be explained hereinbelow by way of anembodiment with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is a cross-section taken through the steering gear housing inparallel to the steering shaft,

FIG. 2 is a cross-section taken through steering gear housing and valvehousing in parallel to the gear rack, and

FIG. 3 is a cross-section of a pump which can be used in the presentinvention to provide fluid pressure.

DETAILED DESCRIPTION OF THE INVENTION

Like parts have been assigned like reference numerals in all Figures.All Figures will be described jointly.

The steering shaft 1, which is non-rotatably coupled to a steering wheel(not shown), can be seen in the drawing. The steering shaft 1 isprovided with an integral pinion 2 in the embodiment shown. The pinion 2is engaged with the gear rack 3 which extends perpendicular to thedrawing plane and is coupled at its ends with the guide rods of thewheels to be steered (not shown). Steering shaft 1 and gear rack 3 arearranged in a common steering gear housing 4. Through the spring 6 andthe retaining element 7, the gear rack 3 is supported in the thrustmember 5 in relation to the steering gear housing 4.

The steering shaft 1 is rotatably supported in a sleeve 9 by way of tworoller bearings 8. In turn, the sleeve 9 is pivotally supported in thesteering gear housing 4 by two needle bearings 10 and two insert rings11 which are rigidly coupled to the steering gear housing 4. The needles12 of the needle bearings 10 are retained in bores 13 of the insertrings 11. By an annular extension 14, the sleeve 9 takes, in each case,support on each needle 12 and is fixed in its position by the force ofthe spring 6. It is essential that the axis of the needle bearings 10,the center line of the steering shaft 1 and the point of forcetransmission from the pinion 2 to the gear rack 3 lie in one plane, andthat the needle bearing axis is more remote from the steering shaft 1than this point of force transmission, while both are disposed on thesame side of the steering shaft 1.

A radial extension 15 is screwed into a threaded bore 16 of the sleeve 9on the side of the sleeve 9 opposite from the gear rack. This extension15 is arranged perpendicular to the steering shaft 1 and perpendicularto the gear rack 3. The other end of the extension 15 is designed as aspherical head 17 and is received in a recess 18 of the valve slide 19of the steering valve which is designed as a linear slide valve. Thehousing 20 of the steering valve is attached to the steering gearhousing 4. The valve slide 19 extends parallel to the gear rack 3.

FIG. 2 shows the cross-section taken along line 2--2 in FIG. 1. Thevalve housing 20 has a port 21 which connects to a hydraulic pump, aport 22 which is pressurized on steering to the right, and a port 23which is pressurized on steering to the left. All three ports 21, 22, 23are interconnected in the neutral position which is illustrated. Thedirection in which the sleeve 9 rotates with the steering shaft 1 duringsteering is indicated by small arrows and the letters R and L.

The captivated spring 24 on the valve slide 19 can be seen on theright-hand side in the housing 20. It is captivated between the stops 25and 26 and will come into abutment on the insert 27 on the housing whenthe slide 19 displaces. In addition, the spring 24 exhibits a highlyprogressive characteristic curve. The insert 27 comprises a port 28which serves as a return port. The valve housing 20 can be completelypreassembled. By means of the screw 29, the insert 27 can be fixed inrelation to the housing 20 after adjustment of the valve slide 19 withthe captivated spring 24. The attachment of the valve housing 20 on thesteering gear housing 4 takes place when both the valve slide 19 and thesteering shaft 1 with the sleeve 9 are in their mid-position.

The operation of the inventive device will now be described. To beginwith, the steering movement is introduced into the gear rack 3 via thesteering shaft 1 and the pinion 2. However, since the gear rack 3 iscoupled to the wheels and the wheels initially stick to their directionbecause of their friction contact on the road surface, the gear rack 3,too, remains stationary. The steering shaft 1 which, through the sleeve9, is supported pivotally in relation to the steering gear housing 4rolls off on the gear rack 3 under these circumstances. In doing so, itentrains the sleeve 9, which, in turn, entrains the extension 15.Depending on the direction of rotation of the steering motion which isintroduced, the spherical head 17, coupled to the valve slide 19, willthus move forward or rearward--into or out of the drawing plane--andthus controls the fluid flow in the valve which causes the auxiliaryforce. The rotary motion of the sleeve 9 is restricted since it willabut on the insert rings 11 after a rotation of a few degrees. As soonas the possibility of tilting about the needle bearings 10 has ended andthe auxiliary force acts, the steering shaft 1 rotates exclusively inthe slide bearings or, respectively, roller bearings 8 and displaces thegear rack 3. When the auxiliary force fails, a small clearance must beovercome solely at the beginning of the steering maneuver. Normalsteering--without boosting--is possible subsequently.

Another advantage of the present invention is that the auxiliary forceis controlled in response to the steering resistance. For instance, athigh speed, when the wheels offer only little resistance to the steeringmovement, the steering shaft 1 will not roll off the gear rack 3. Thisis assisted, in addition, by the captivated spring 24. The steeringshaft 1 rotates only in the sleeve 9, and a steering maneuver isperformed which is not power-assisted. This also applies on slipperyground, e.g. on ice or snow.

Referring to FIG. 3, which is a cross-section of a pump which can beused in the power steering system of the present invention to providefluid under pressure, the housing 30 is stationary in that it is rigidlyattached to the steering gear housing 4 of FIG. 1, while the rotor 31 isrotatably supported on a control shaft 33 which, in turn, is fixed tothe housing 30. Pistons 34 are guided in bores 36 in the rotor 31 andtake support on the inside surface of the external ring 32 via balls 35.

The control shaft 33 is provided with control grooves 37, 38 which arein communication with pressure lines 41, 42 which, in turn, areconnected with the chambers of a hydraulic cylinder 40 of the steeringsystem. Pressure fluid is contained in the pressure lines in the pumpand the hydraulic cylinder. The external ring 32 can be moved to theleft and to the right, respectively. A recess 18 is provided for thispurpose into which the spherical head 17 of the extension 15 of FIGS. 1and 2 is fitted, thereby varying the eccentricity of the pump. Theeccentricity is zero in FIG. 3, since rotor 31 and external ring 32 arearranged concentrically. In this position, there is no radial movementof the piston 34 while the rotor 31 is rotating, and the pump does notdeliver fluid.

Once the external ring 32 is displaced so that the eccentricity is nolonger zero, the pistons 34 in the rotating rotor 31 undergo radialmovement and hence deliver pressure fluid from pressure line 41 intopressure line 42 in respect of the one direction of displacement of theexternal ring 32 and vice-versa in respect of the other direction. Thismeans that in the event of a given direction of rotation and a givenrotational speed of the rotor 31, the piston 43 in the double-actinghydraulic cylinder 40 can be readjusted to assume any position desiredby varying the eccentricity, namely the position of external ring 32.

An electric switch (or sliding contact or potentiometer or sensor) canbe included in the power steering system of the present invention tocontrol the supply of pressure fluid such that pressure fluid isavailable only when the linear slide control valve is displaced from itsinactive position, namely when pressure fluid is required. This can beeffected by switching on/off a pump via an electric switch or via theadjustment of the rotational speed of a pump (e.g. via a potentiometer).The pump operation can be controlled by movement of the linear slidecontrol valve or the valve control means, namely extension 15. Bydisconnecting the source of pressure fluid when no pressure fluid isneeded, energy is conserved.

List of Reference Numerals

1--steering shaft

2--pinion

3--gear rack

4--steering gear housing

5--thrust member

6--spring

7--retaining element

8--roller bearing

9--sleeve

10--needle bearing

11--insert ring

12--needle

13--bore

14--annular extension

15--extension

16--threaded bore

17--spherical head

18--recess

19--valve slide

20--valve housing

21--port

22--port

23--port

24--captivated spring

25--stop

26--stop

27--insert

28--port

29--screw

30--housing

31--rotor

32--external ring

33--control shaft

34--pistons

35--balls

36--bores

37--control groove

38--control groove

40--hydraulic cylinder

41--pressure line

42--pressure line

43--piston

I claim:
 1. A device for actuating a hydraulic power steering system forautomotive vehicles inhering the following features:a steering shaftnon-rotatably coupled with a steering wheel is furnished with a pinionand is supported in a sleeve, the pinion is engaged with a gear rackcoupled to wheels to be steered, the sleeve is supported in a steeringgear housing so as to be pivotable about a parallel axis in relation tothe steering shaft, and it comprises a recess to enable the pinion toengage into the gear rack, and on it a pin-shaped extension is securedvertically relative to the steering shaft, the extension actuating avalve slide of a steering valve designed as a linear slide valve, aspring which presses the gear rack against the pinion simultaneouslystabilizes the support of the sleeve in the steering gear housing,characterized by the following further features: two needle bearingsbetween the sleeve and the steering gear housing are formed by twoneedles, the two needle bearings are designed on different sides of thegear rack, the bearing axis interconnecting the two needle bearings isfarther away from the steering shaft center line than the point of forcetransmission between the pinion and the gear rack, and it is placed onthe same side of the steering shaft center line as the latter point(both axes and the point lie in one plane), and the valve slide isbiassed by a captivated spring.
 2. A device as claimed in claim 1,characterized by the further feature of a pair of insert rings which arerigidly coupled to the steering gear housing and within which theneedles are individually retained.
 3. A device as claimed in claim 1,characterized by the further features of a spring and the sleeve havingan annular extension which is retained by the spring in relation to eachneedle.
 4. A device as claimed in claim 2, characterized in that theinsert rings simultaneously serve as limiter (stops) for the rotarymotion of the sleeve about the bearing axis.
 5. A device as claimed inclaim 1, characterized in that the extension is screwed into a threadedbore of the sleeve.
 6. A device as claimed in claim 5, characterized inthat the extension extends vertically relative to the gear rack.
 7. Adevice as claimed in claim 6, characterized in that the end of theextension which is not coupled to the sleeve is furnished with aspherical head and engages into a recess of the valve slide.
 8. A deviceas claimed in claim 1, characterized in that a housing of the steeringvalve is rigidly coupled to the steering gear housing.
 9. A device foractuating a hydraulic power steering system for automotive vehiclescharacterized by the following features:a steering shaft non-rotatablycoupled with a steering wheel is furnished with a pinion and issupported in a sleeve, the pinion is engaged with a gear rack coupled towheels to be steered, the sleeve is supported in a steering gear housingso as to be pivotable about a parallel axis in relation to the steeringshaft, and it comprises a recess to enable the pinion to engage into thegear rack, and on it a pin-shaped extension is secured verticallyrelative to the steering shaft, the extension governing the eccentricityof a pump which acts upon a double-effect hydraulic cylinder assistingthe movement of the gear rack, a spring which presses the gear rackagainst the pinion simultaneously stabilizes the support of the sleevein the steering gear housing, two needles form two bearings between thesleeve and the steering gear housing on different sides of the gearrack, the bearing axis interconnecting the two needle bearings isfarther away from the steering shaft center line than the point of forcetransmission between the pinion and the gear rack, and it is placed onthe same side of the steering shaft center line as the latter point, aswell as in one plane with the two of them.
 10. A device for actuating apower steering system for automotive vehicles characterized by thefollowing features:a steering shaft non-rotatably coupled with asteering wheel is furnished with a pinion and is supported in a sleeve,the pinion is engaged with a gear rack coupled to wheels to be steered,the sleeve is supported in a steering gear housing so as to be pivotableabout a parallel axis in relation to the steering shaft, and itcomprises a recess to enable the pinion to engage into the gear rack,and on it a pin-shaped extension is secured vertically relative to thesteering shaft, the extension actuating an electric switch, a slidingcontact, a potentiometer or sensor for controlling the power-assistedsteering system, a spring which presses the gear rack against the pinionsimultaneously stabilizes the support of the sleeve in the steering gearhousing, two needle bearings between the sleeve and the steering gearhousing are formed by two needles, the two needle bearings are designedon different sides of the gear rack, and the bearing axisinterconnecting the two needle bearings is farther away from thesteering shaft center line than the point of force transmission betweenthe pinion and the gear rack, and it is placed on the same side of thesteering shaft center line as the latter point as well as in one planewith the two of them.
 11. Apparatus for actuating a linear slide controlvalve of a hydraulic power steering system in response to rotation of asteering wheel of an automotive vehicle, aid apparatus comprising:asteering gear housing; a gear rack within said steering gear housing andadapted to be coupled to a pair of wheels of said automotive vehicle; asteering shaft adapted to be coupled to a steering wheel of saidautomotive vehicle and having a pinion engaging said gear rack anddisposed perpendicular to said gear rack; a sleeve through which saidsteering shaft extends and within which said steering shaft can rotaterelative to said sleeve; first and second bearing means for mountingsaid sleeve in said steering gear housing for pivotal movement of saidsleeve relative to said steering gear housing, each of said bearingmeans including:(a) a needle pin mounted to said steering gear housing,and (b) a needle bearing mounted to said sleeve and engaged by one ofsaid needle pins; said first and said second bearing means located:(a)on opposite sides of said gear rack and having a common axis whichextends parallel to said steering shaft, and (b) on the same side ofsaid steering shaft as the engagement of said pinion and said gear rackand radially outward of the engagement of said pinion and said gearrack; a linear slide control valve having an inlet means adapted forconnection to a source of pressure fluid for receiving pressure fluidand outlet means adapted for connection to a power drive for dispensingpressure fluid; and valve control means extending between said sleeveand said linear slide control valve for controlling said linear slidecontrol valve in response to pivotal movement of said sleeve.
 12. Apower steering system according to claim 11 further including means forurging said gear rack and said pinion into engagement.
 13. A powersteering system according to claim 12 wherein said linear slide controlvalve includes a valve slide movable along a line extending parallel tothe movement of said gear rack and said valve control means include amember fixed to said sleeve and extending perpendicular to said steeringshaft.
 14. A power steering system according to claim 13 wherein saidsteering gear housing includes first and second insert rings at oppositeends of said steering gear housing and said needle pins are mounted insaid insert rings.
 15. A power steering system according to claim 14wherein said needle bearings are formed in extensions at opposite endsof said sleeve.
 16. A power steering system according to claim 14wherein said insert rings have stops which define the extent to pivotalmovement of said sleeve.
 17. A power steering system according to claim13 wherein said sleeve has a tapped bore and said valve control memberhas a threaded end which is turned into said tapped bore.
 18. A powersteering system according to claim 17 wherein said valve control memberextends perpendicular to said gear rack.
 19. A power steering systemaccording to claim 18 wherein said valve slide has a recess and saidvalve control member has a spherical head at an end opposite saidthreaded end which is received by said recess in said valve slide.
 20. Apower steering system according to claim 19 wherein said linear slidecontrol valve has a housing which is attached to said steering gearhousing.
 21. A power steering system according to claim 11 wherein saidcommon axis and the engagement of said pinion and said gear rack bothare in one plane.
 22. A power steering system according to claim 11wherein said common axis, the engagement of said pinion and said gearrack, and the axis of said steering shaft all are in one plane. 23.Apparatus for governing the eccentricity of a pump which controls adouble-acting cylinder of a hydraulic power steering system in responseto rotation of a steering wheel of an automotive vehicle, said apparatuscomprising:a steering gear housing; a gear rack within said steeringgear housing and adapted to be coupled to a pair of wheels of saidautomotive vehicle; a steering shaft adapted to be coupled to a steeringwheel of said automotive vehicle and having a pinion disposedperpendicular to said gear rack and engaging said gear rack for movingsaid gear rack in response to rotation of said steering shaft; a sleevethrough which said steering shaft extends and within which said steeringshaft can rotate relative to said sleeve; first and second bearing meansfor mounting said sleeve in said steering gear housing for pivotalmovement of said sleeve relative to said steering gear housing, each ofsaid bearing means including:(a) a needle pin mounted to said steeringgear housing, and (b) a needle bearing mounted to said sleeve andengaged by one of said needle pins; said first and said second bearingmeans located:(a) on opposite sides of said gear rack and having acommon axis which extends parallel to said steering shaft, and (b) onthe same side of said steering shaft as the engagement of said pinionand said gear rack and radially outward of the engagement of said pinionand said gear rack; a double-acting cylinder coupled to said gear rackfor assisting movement of said gear rack in response to rotation of saidsteering shaft; a pump adapted for connection to a source of pressurefluid for dispensing pressure fluid to drive said double-actingcylinder; and means extending between said sleeve and said pump forgoverning the eccentricity of said pump in response to pivotal movementof said sleeve.
 24. Apparatus for controlling the power drive of ahydraulic power steering system in response to rotation of a steeringwheel of an automotive vehicle, said apparatus comprising:a steeringgear housing; a gear rack within said steering gear housing and adaptedto be coupled to a pair of wheels of said automotive vehicle; a steeringshaft adapted to be coupled to a steering wheel of said automotivevehicle and having a pinion disposed perpendicular to said gear rack andengaging said gear rack for moving said gear rack in response torotation of said steering shaft; a sleeve through which said steeringshaft extends and within which said steering shaft can rotate relativeto said sleeve; first and second bearing means for mounting said sleevein said steering gear housing for pivotal movement of said sleeverelative to said steering gear housing, each of said bearing meansincluding:(a) a needle pin mounted to said steering gear housing, and(b) a needle bearing mounted to said sleeve and engaged by one of saidneedle pins; said first and said second bearing means located:(a) onopposite sides of said gear rack and having a common axis which extendsparallel to said steering shaft, and (b) on the same side of saidsteering shaft as the engagement of said pinion and said gear rack andradially outward of the engagement of said pinion and said gear rack;drive means coupled to said gear rack for assisting movement of saidgear rack in response to rotation of said steering shaft; a pump adaptedfor connection to a source of pressure fluid for dispensing pressurefluid to said drive means; control means for controlling operation ofsaid pump; and means extending between said sleeve and said controlmeans for actuating said control means to control operation of said pumpin response to pivotal movement of said sleeve.